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Drugs Acting on the Intestines (view source)
Revision as of 11:30, 5 November 2008
, 11:30, 5 November 2008→Drugs Decreasing Smooth Muscle Contractility
==Drugs Decreasing Smooth Muscle Contractility==
==Drugs Decreasing Smooth Muscle Contractility==
These drugs are used to treat conditions associated with smooth muscle spasms or diarrhoea.
====Muscarinic Receptor Antagonist====
Examples are '''hyoscine, atropine''' and '''propantheline'''. '''Buscopan''' is a preparation commonly used in large animal medicine that contains hyoscine and the analgesic, dipyrone. They are all administered by injection.
They work by competitively inhibiting the effect of acetylcholine on the intestinal smooth muscle muscarinic receptors. This results in decreased motility and intestinal mucus secretions. It has no effect on fluid secretions. It has a lack of selectivity and so any side effects experienced are due to it's actions on muscarinic receptors at other sites around the body.
'''It is used to help reduce smooth muscular spasms in the gastrointestinal tract.'''
====Opioid Receptor Agonists====
Examples are '''loperamide, diphenoxylate''' and '''codeine''', which are administered orally.
They work by mimicking the action of endogenous endorphins and enkephalins. This results in an increase of transit time of ingesta through the gastrointestinal tract. This allows more time for absorption of fluid; combining this action with it's ability to decrease intestinal fluid secretions it is often a good treatment for diarrhoea.
Loperamide works for prolonged periods on the gastrointestinal tract, as it undergoes enterohepatic recycling. Though it is poorly absorbed and won't cross the blood-brain barrier and so will have no CNS side-effects.
Diphenoxylate is better absorbed than loperamide but doesn't have any effects on the CNS.
Care should be used when given to cats as they cause hyperexcitability on overdose.
==Other Drugs==
==Other Drugs==